Conventionally, there has been known an energy storage device having the configuration where the energy storage device includes an electrode assembly having stacked plates and current collectors, and the stacked plates and the current collectors are joined to each other. For example, JP 2016-189323 A discloses an energy storage device having the configuration where projecting portions of an electrode assembly, lug portions of the current collectors and opposedly facing lugs of clip members are joined to each other by fitting engagement.